Though organic light-emitting diodes, or OLEDs, hold significant potential as a light source with unique application potential, designers will have to continue to wait before the technology is ready for mainstream architectural lighting use. Because of OLEDs’ low luminance and diffused output, their applications to date have been limited to signage backlighting, sculptural installations, and conceptual prototypes. The dearth in demand has kept OLED prices high and research and development budgets low as manufacturers focused instead their attention on LEDs and improving the quality and efficacy of those point sources.
But OLEDs are attracting growing interest from lighting designers because of their simplicity, says Giana Phelan, director of business development at Rochester, N.Y.–based OLEDWorks, which acquired Philips’ OLEDs business division and Lumiblade platform in 2015. “People are [experiencing] LED overload,” she says. “They’ve had to learn a lot about waveguides and diffusers for LEDs. In comparison, OLEDs are pretty easy. They don’t need anything but a driver and [a designer’s] creativity.”
LEDs Versus OLEDs
LED and OLED technologies had measurable penetration in the architectural market around 2006 and 2011, respectively, estimates Naomi Miller, a designer and senior scientist at the U.S. Department of Energy’s (DOE’s) Pacific Northwest National Laboratory (PNNL), in Richland, Wash. Though they are both solid-state lighting, based on semiconductor technology, their similarities for the most part end there.
An LED is comprised of two electrodes—a cathode and an anode—that produce light when current is applied. Color temperature is determined by the type of semiconductor materials used.
By contrast, an OLED consists of layers of an organic (or carbon-based) compound, such as organometallic fluorescent chelates or electroluminescent polymers, sandwiched between the cathode and anode, and deposited on a substrate—typically rigid glass although some flexible materials and roll-to-roll plastics are in development. The organic materials determine the color temperature. The lack of manufacturing lines dedicated to making large OLED panels has limited their availability to small sizes, such as 2 inches square, 4 inches square, or 2 inches by 8 inches.
As in all semiconductor manufacturing, costs are high when the fabrication process is new and volumes are low. Achieving economies of scale requires strong demand, which has yet to materialize for OLEDs. Although the past five years have seen some developments in the technology, few architectural fixtures are commercially available, according to PNNL’s May 2016 report, “OLED Lighting Products: Capabilities, Challenges, Potential.”
According to the DOE’s “Solid-State Lighting R&D Plan,” published in June 2016, a best-in-class LED downlight in 2015 produced 64 lumens per watt (lm/W) and cost $29 per kilolumen. Meanwhile, a best-in-class OLED luminaire produced 43 lm/W and cost $870 per kilolumen, 30 times the cost of the LED.
However, the simplistic comparison is unfair for several reasons, says Miller, along with PNNL electrical engineer Felipe Leon. Miller notes that an OLED luminaire would likely serve as a sculptural piece, while an LED downlight, which is mass produced and an established technology, would serve utilitarian purposes. “Think of comparing a basic ceiling light fixture with a chandelier,” Leon adds.
A more telling indicator may be the unit price of an OLED panel itself. The DOE R&D plan notes that the 2016 manufacturing cost is $1,850 per square meter. That needs to drop dramatically for OLED lighting to become commercially viable; the DOE is targeting a cost of $100 per square meter by 2025, according to the report.
OLED Advantages
Still, OLEDs are appealing in architectural applications for several reasons. Whereas LEDs are points of directional light, OLED panels emit a uniform amount of soft illumination evenly diffused across their entire surface, with minimal glare. Unlike LEDs, they are cool enough to touch because the heat is distributed across a larger surface. They are also lightweight and extremely thin—less than 2 millimeters thick—and distribute light with a wide beam angle. As such, OLED panels are versatile and can be installed horizontally or vertically, and illuminate a relatively large space.
OLED fixtures also don’t need as many components as their LED counterparts, which require heat sinks and optical devices, such as diffusers, lenses, and shades. An OLED panel is innately a diffuse source that does not need a heat sink. “With OLEDs, the panel is the luminaire,” Miller says.
Finally, OLEDs can be deposited on flexible substrates and thus can be configured into nearly any shape. They even can be made into a mirror or completely transparent so that they emit light from both faces.
Barriers to Entry
Besides cost, OLED technology faces competition in life expectancy and efficacy from LEDs. Although OLEDs have listed lifetimes of 40,000 hours at a luminance of 3,000 candela per square meter—acceptable for decorative lighting—panels pushed to higher luminance levels tend to expire earlier, according to the DOE’s “OLED Lighting Products” report. A panel operated at 8,300 candela per square meter—a level appropriate for desktop tasklighting—may have an operating life of 10,000 hours, or 2.5 years.
Efficacy is another challenge. Miller estimates that today’s OLED products emit 20 lm/W to 60 lm/W at the panel level, a spec that hasn’t budged much in several years. OLEDs’ current extraction efficiency is 30 to 35 percent, according to the DOE’s R&D plan. The agency would like that number to hit 70 percent by 2020. The OLED industry is currently improving light extraction methods, including films applied to the OLED glass substrate. Internal or external extraction methods alone can increase the efficacy of an OLED panel by a factor of two or more, Miller says.
The selection of drivers not designed for OLEDs’ electrical properties also contributes to their inefficiencies. After dissecting several OLED products on the market, Leon found some using two drivers, one for “converting to a voltage, and the other [an OLED driver to provide] the appropriate current level to … allow for dimmability,” he says. He believes luminaire manufacturers “may incorporate added value technology to their OLED products” to justify their cost premium. However, if drivers can be developed to complement the specific electrical characteristics of OLEDs, the panels’ overall operation will improve.
Meanwhile, the rapid evolution of LEDs continues. In fact, OLEDs’ chief competition today is edge-lit optics, in which LEDs placed along the edge of a panel—typically a plastic, such as polycarbonate or acrylic—use etching, diffusers, and waveguides to distribute light across the surface. Edge-lit panels are thicker than an OLED panel, at about 9 millimeters.
Manufacturers have also started to develop hybrid LED/OLED fixtures that “boost the light output and reduce cost per lumen while maintaining the aesthetic appeal of OLED luminaire designs,” write the DOE R&D plan’s authors. These first generation product offerings include Acuity Brands’ Duet SSL Technology and WAC Lighting’s Hybrid OLED/LED luminaire.
Recent Developments
OLEDs could achieve the DOE’s goals as manufacturers ramp up production of displays for mobile devices and televisions. Samsung phones, for example, have used such displays for years, OLEDWorks’ Phelan says. “A lot of people are carrying around OLED screens in their pockets, and they don’t even know it.”
Last year, LG transferred its OLED Light Division from LG Chemical to LG Display, which makes screens for electronics. In March, LG Display announced the construction of the “world’s first fifth-generation” OLED light panel factory in Gumi, South Korea, with an initial input capacity of 15,000 1,000-millimeter-by-1,200-millimeter glass substrates per month, starting in 2017.
“The input capacity will increase depending on the market situation,” says Joon Park, vice president of LG Display OLED Light Division; that increase could lead to significant price competitiveness. The company is also investing heavily in additional factories to produce larger television panels and flexible panels for smartwatches and other mobile devices. LG’s OLED Light Division can benefit from these investments, Park adds: “There will be advantages such as integrated purchasing, shared investment, increased productivity, improvement in production infrastructure, and expanded use of technology patents.”
Meanwhile, OLEDWorks’ acquisition of Philips’ OLED lighting division included a factory in Aachen, Germany, capable of manufacturing higher volumes and possessing expertise in the “production of quality high-brightness panels,” said OLEDWorks’ CEO David DeJoy when he announced the acquisition in April 2015.
Both LG and OLEDWorks are currently exploring flexible OLEDs. LG Display demonstrated flexible panels in myriad fixture configurations at Light+Building in 2016. And OLEDWorks has demonstrated a bendable product that uses Corning’s Willow Glass, a flexible glass 100 to 150 microns thick that can be rolled up like a sheet of paper.
While OLEDs face barriers, the technology is still in its infancy. LED lighting, in its early years, struggled with many of the same difficulties. The difference, according to the PNNL report, is that “OLED manufacturers have the advantage of having watched and learned from the LED industry working through these problems.” As such, OLEDs will likely become a dynamic and versatile source for lighting designers in due time. •
Resources
An introductory list of references on OLED technology and products.
“Solid-State Lighting R&D Plan,” by the U.S. Department of Energy, June 2016.
“OLED Lighting Products: Capabilities, Challenges, Potential,” by the U.S. Department of Energy, Pacific Northwest National Laboratory, May 2016.
“2014 Status Report on Organic Light Emitting Diodes,” by the European Commission, Joint Research Centre, 2014.
“Five Products and Trends Shaping the Market for OLED Lighting,” by Hallie Busta, Architectural Lighting, March 31, 2015.
